I've just noticed something that might help nail down the problem, maybe: When I'm at home and do a WiFi scan, it shows "Scanning", with the WiFi SSID I'm connected to. When the scan fails, the screen turns from orange to grey, then shrinks and has a "Try Again" button. Above that button, it shows - not my current SSID, but the SSID of my WiFi at work (which does pass scan)! Given that work is over 35 miles away and I can't possibly be connected to its WiFi, I find this rather peculiar. Again, I cleared all my caches, but it's still doing it.